1. Field of the Invention
The present invention relates to an image sensing apparatus, a signal detection apparatus, and a signal accumulation apparatus and, more particularly, to read control of a signal from a pixel or cell.
2. Related Background Art
FIGS. 1A and 1B are equivalent circuit diagrams, respectively, showing the pixel portions of conventional two-dimensional solid-state image sensing apparatuses. In FIGS. 1A and 1B, the circuits respectively comprise power supply lines 1, reset switch lines 2, selection switch lines 3, signal output lines 4, and photodiodes 5. The circuit in FIG. 1A also includes a transfer switch line 6. FIG. 1A shows the circuit of the solid-state image sensing apparatus reported by Eric R. Fossum et al., IEDM, 1993 (technical reference 1: IEDM 93, pp. 583-586). FIG. 1B shows the circuit of the solid-state image sensing apparatus reported in xe2x80x9cISSCC96/Session 1/Plenary Session/Paper TA1.2xe2x80x9d. FIG. 2 shows an example of the circuit in FIG. 1B in which pixels are two-dimensionally laid out, and a read circuit for reading out an image signal is added.
Such a two-dimensional solid-state image sensor including a signal amplifier within each pixel requires a plurality of switch elements and a plurality of elements constituting the signal amplifier in addition to the photodiode. In FIG. 1A, one pixel requires one photodiode and four MOS transistors, inevitably increasing the size of one pixel.
The basic operation of the circuit in FIGS. 1A and 2 will be described.
(1) A reset operation of inputting the reset voltage to the input node of a source follower Q3 is performed by a reset switch Q2, and a row is selected by a selection switch Q4.
(2) The input node of the source follower Q3 is floated. A noise component made up of reset noise and fixed pattern noise such as variations in threshold voltage of the MOS source follower Q3 is read out, and the readout information is temporarily held in a signal accumulator 15.
(3) A transfer switch Q1 is opened/closed to transfer an accumulation charge generated by an optical signal to the input node of the source follower Q3. The sum of the noise component and the optical signal component is read out and held in the signal accumulator 15.
(4) The signal of the noise component and the signal of the noise and optical signal components are respectively read out to common signal lines 19 and 19xe2x80x2 via common signal line transfer switches 18 and 18xe2x80x2. Outputs from the common signal lines 19 and 19xe2x80x2 respectively yield outputs 13 and 14 via buffer amplifiers. In the next stage, the reset noise and the fixed pattern noise can be removed by calculating the difference between the outputs 13 and 14. Note that pixels are sequentially scanned by a vertical shift register 12 and a horizontal shift register 16.
To the contrary, in FIG. 1B, one pixel requires one photodiode and three MOS transistors. The number of transistors is smaller by one than in FIG. 1A, and the transfer switch line can be eliminated. This significantly reduces the pixel size.
However, owing to the absence of the transfer switch, the pixel of FIG. 1B does not comprise the mechanism of holding the noise component of each pixel during the accumulation period. Accordingly, noise cannot be removed, and the signal component-to-noise component ratio, i.e., S/N ratio of the image sensing apparatus is lower than in FIG. 1A.
As described above, in the prior arts, it is difficult to realize a high S/N ratio and reduce the pixel size. In addition, the dynamic range narrows upon voltage drop of the selection switch Q4.
It is an object of the present invention to reduce the size of a pixel or cell.
It is another object of the present invention to prevent a decrease in dynamic range of the pixel.
To achieve the above objects, according to an embodiment of the present invention, there is provided an image sensing apparatus comprising a plurality of pixels each including photoelectric conversion means, amplification means for amplifying a signal from the photoelectric conversion means, transfer means for transferring the signal from the photoelectric conversion means to the amplification means, and read control means for controlling a read of the signal from the amplification means under control of a voltage level of an input portion of the amplification means.
According to another embodiment, there is provided a signal detection apparatus comprising a plurality of cells each including detection means, amplification means for amplifying a signal from the detection means, transfer means for transferring the signal from the detection means to the amplification means, and read control means for controlling a read of the signal from the amplification means under control of a voltage level of an input portion of the amplification means.
According to still another embodiment, there is provided a signal accumulation apparatus comprising a plurality of cells each including accumulation means, amplification means for amplifying a signal from the accumulation means, transfer means for transferring the signal from the detection means to the accumulation means, and read control means for controlling a read of the signal from the amplification means under control of a voltage level of an input portion of the amplification means.
With the above arrangement, the size of the pixel or cell can be reduced.
The pixel can attain a wide dynamic range.
Other objects and features of the present invention will be apparent from the following description in conjunction with the accompanying drawings.